This invention relates to large size, shaft type, rock excavating machines and, more particularly, to down-the-hole type shaft excavating machines capable of forming, being suspended in and movable along a vertical shaft in a rock formation.
While large size boring machines have been heretofore successfully developed for cutting generally horizontally extending tunnels, at the present time there has been limited development of large size shaft boring machines for cutting generally vertically extending shafts. Although tunnel boring machines and shaft boring machines involve some common requirements and problems, such as the capability of excavating various types and quality of rock strata at the bore site, they have even more non-common requirements and problems. Thus, tunnel boring technology has not heretofore provided a satisfactory solution to mechanized shaft sinking problems.
Shaft sinking is one of the most time consuming, costly and hazardous operations in opening a new mine or providing additional access to an expanding mine. With few exceptions, shafts sunk today are excavated by drilling and blasting--a method which has been the practice for over a hundred years. The prior art has included a mechanical lashing device which enables the muck to be removed as fast as powerful hoisting systems can handle it. Such operations are heavily labor intensive, requiring as many as 60 laborers on the shaft bottom during the drilling cycle. The method has since improved with delay detonators, hydraulic drill jumbos, and improved mechanical mucking machines, but it is still labor intensive and at times, provides such poor working conditions due to noise, heat, dirt and fumes, that it is becoming increasingly difficult to find miners willing to work in the shafts.
Because some existing tunnel boring machines can bore at rates of over 200 feet per day, and because of the similarity of shaft and tunnel construction, the application of tunnel boring technology to shaft sinking has been given previous consideration. Many of the shaft sinking devices borrowing from tunnel boring technology, require a pilot hole for the cuttings to fall through for muck removal.
It can be seen that a substantial effort has been devoted to the mechanization of shaft sinking in the last two decades. Competition due to mining of more favorable mineral deposits, scarcity of experienced personnel, decreasing willingness of personnel to do physical work, and larger and deeper shafts have caused machinery manufacturers and contractors alike to attempt to make improvements in mechanization of shaft sinking. The past trend in mechanization of shaft sinking has been to larger and larger drills.
The need for improvements in shaft excavation technology has been expounded in nearly every mining related journal or technical meeting over the last several years. Millions of dollars are being spent annually by industry and government alike to advance the state of the art. This recent interest stems from several activities. They are: coal mining, metal mining, oil mining, military and defense, pumped storage and nuclear waste isolation.
Recent estimates of shaft demand for coal mining in the U.S. are that 340 to 470 shafts greater than 1000 ft. will be excavated between 1980 and 1990. Although the present world economy has slowed many mining projects, if not deferred them indefinitely, other related underground projects have begun to gather momentum. Nuclear waste isolation, pumped storage and military programs are a few of these upcoming projects.
There are a variety of shaft excavation methods including drilled shafts, bored shafts, conventional shafts, raised shafts, round shafts, elliptical shafts, square shafts, and inclined shafts. This invention relates particularly to down-the-hole blind shaft boring machines, although it is equally adapted to non-blind shafts with a pilot-hole as well.
Prior art blind shaft boring machines have all been unsatisfactory with respect to the major problem of removal of cuttings, which is referred to as mucking. It is necessary that any machine be capable of lifting the cuttings reliably from the shaft bottom to a point above the machine.
Successful usage of prior art shaft boring machines has required a pre-drilled pilot hole for muck removal at a substantial increase in cost and time of the sinking operation. Prior art attempts to develop a successful down-the-hole shaft boring machine have been based on the common concept that tunnel boring machines could be stood upright to sink shafts. The basic problems associated with using tunnel boring machine designs for shaft boring machines are as follows:
Full Face Cutting--most prior art shaft boring machines have used full face cutter wheels to excavate the shaft bottom whereby the diameter of the cutter wheel is substantially the same as the diameter of the shaft. A full face cutter wheel severly restricts the machines' mucking ability since all cut material must be directed to a singular or possibly multiple pickup point(s) in the cutter wheel. Questions relating to safety are also raised when one considers changing cutters on a full face shaft boring machine, since workmen must be below the machine during installation. Even with the advent of rear or side mounted cutters, the cutter wheel must be blocked off the shaft bottom to take the loads off the cutters. If a pilot hole exists in the shaft, care must be taken to prevent workers or cutters from falling down the hole during repairs or changes. PA1 In blind shafts, water control is also a problem. Shafts are similar to large water wells and unless water pumps can be set at shaft bottom, the water will seriously affect the muck gathering ability of the cutter wheel and greatly reduce cutter life. Water control is a very important activity in shaft sinking. Unless suitable means are provided for water control, the blind shaft boring machine is in constant danger of being flooded. PA1 Massive Structure--A massive structure is necessary to transmit the thrust and torque required to efficiently cut a full face of rock. This structure severly restricts the space available for the placement of a suitably sized mucking system through the machine. This structure also restricts access to the shaft bottom for water control, grout drilling, and/or probe drilling. PA1 Gripper Pads--tunnel boring machines use gripper pads to grip the side of the tunnel and react to the machines' thrust and torque. When shaft boring machines use gripper pads, problems are encountered because the pad pressure required is too high. Shaft sinking, by its nature, traverses many geological formations with crushed rock and shear zones probable at each formation boundary. Pad pressures for shaft boring machines should be considerably lower than for tunnel boring machines so the machine may be secured in very weak rock. PA1 Size, Weight and Cost--The application of tunnel boring machine technology to shaft sinking has resulted in shaft boring machines with tunnel boring machine specifications and rate of penetration capabilities. Conventional shaft sinking rates are typically 3 to 6 meters per day. Tunnel boring machines have been designed with the power to advance 30 to 60 meters a day but cannot be utilized at such high rates for shaft sinking because muck handling, hoisting and lining systems cannot keep up with such a high rate of advance. The high capital costs associated with the tunnel style machines are also a problem since the contractor-owner must amortize the machine cost over a shaft excavation length which is typically 1/10 to 1/20 the length of machine bored tunnels. Any shaft boring machine must be removed from the bottom of the shaft at the completion of the shaft sinking operation. Because of hoisting limitations from shaft depths, heavy machine components are undesirable. Thus, the machine must be manufactured with smaller, lighter pieces which are bolted together. This increases the cost of the machinery above conventional tunnel boring machine price levels.
Thus, a general object of the present invention is to provide a shaft boring machine which is functionally effective, suitable for the environment it must work in, lightweight and low in price.